Article pubs.acs.org/est
Bioaccessibility of Arsenic in Mining-Impacted Circumneutral River Floodplain Soils Christian Mikutta,*,† Petar N. Mandaliev,† Nina Mahler,† Tsvetan Kotsev,‡ and Ruben Kretzschmar† †
Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, CHN, ETH Zurich, 8092 Zurich, Switzerland Department of Geography, National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
‡
S Supporting Information *
ABSTRACT: Floodplain soils are frequently contaminated with metal(loid)s due to present or historic mining, but data on the bioaccessibility (BA) of contaminants in these periodically flooded soils are scarce. Therefore, we studied the speciation of As and Fe in eight As-contaminated circumneutral floodplain soils (≤21600 mg As/kg) and their size fractions using X-ray absorption spectroscopy (XAS) and examined the BA of As in the solids by in-vitro gastrointestinal (IVG) extractions. Arsenopyrite and As(V)-adsorbed ferrihydrite were identified by XAS as the predominant As species. The latter was the major source for bioaccessible As, which accounted for 5−35% of the total As. The amount of bioaccessible As increased with decreasing particle size and was controlled by the slow dissolution kinetics of ferrihydrite in the gastric environment (pH 1.8). The relative BA of As (% of total) decreased with decreasing particle size only in a highly As-contaminated soil − which supported by Fe XAS − suggests the formation of As-rich hydrous ferric oxides in the gastric extracts. Multiple linear regression analyses identified Al, total As, Corg, and P as main predictors for the absolute BA of As (adjusted R2 ≤ 0.977). Health risk assessments for residential adults showed that (i) nearly half of the bulk soils may cause adverse health effects and (ii) particles
